Physical factors that are responsible for the effect of heat treatment on the magnetic properties of iron-based amorphous alloys

A systematic study is made into the specific influence of heat treatment in the air on magnetic properties of ribbons of amorphous magnetically soft alloys with positive saturation magnetostriction, alloy Fe81B13Si4C2 being taken as an example. It is shown that in addition to an internal stress decrease and a shape effect the formation of an optimum thickness amorphous-crystalline surface layer results in a decrease of orthogonal magnetization domains volume. The surface layer induces predominantly plane tensile stresses in an amorphous matrix. Anisotropic stresses occurring in the ribbon after heat treatment in the air are due to appropriate anisotropic distribution of interstitial elements because of the interaction between a ribbon surface and water vapors from the air. Anisotropic distribution of interstitial elements in a ribbon surface layer is the reason for the occurrence of the anisotropy of surface crystallization rate in the alloy, the latter also induces anisotropic stresses in the ribbon